A typical ferrite surface mount electro-magnetic interference ("EMI") suppressor includes a generally rectangular ferrite body with an electrically conductive path extending therethrough. The electrically conductive path, in turn, is connected to respective conductive coating layers on opposite ends of the ferrite body to facilitate connection to a printed circuit board, for example. Such a ferrite EMI suppressor may commonly be manufactured by printing a plurality of interconnected conductive traces on successive stacked ferrite layers.
U.S. Pat. No. 4,543,553 to Mandai et al. entitled "Chip-Type Inductor" discloses a chip inductor comprising a plurality of laminated magnetic layers. Linear conductive patterns extend between the respective magnetic layers, and these linear conductive patterns are connected successively to define a coil so as to produce an inductance component. The conductive patterns on opposite surfaces of the magnetic layers are connected to each other by through-holes wherein the conductors are deformed to plunge through the holes to establish electrical contact.
Another device is disclosed in U.S. Pat. No. 4,689,594 to Kawabata et al. entitled "Multi-Layer Chip Coil." In this patent a multi-layer chip coil comprises a stack of intermediate laminas of magnetizable material having a through-hole defined therein so as to extend completely through the thickness thereof. First and second patterned electrical conductors are formed on the opposite surfaces of each of the intermediate laminas, and a hollow tubular conductive layer extends through the through-hole so as to connect adjacent conductors.
Still another device is disclosed in U.S. Pat. No. 5,302,932 to Person et al. entitled "Monolithic Multilayer Chip Inductor and Method For Making Same." This patent discloses a monolithic multilayer chip inductor which includes a plurality of subassemblies stacked one above another. Each of the intermediate subassemblies includes a ferrite layer having a coil conductor with a uniform width printed on its upper surface. The intermediate ferrite layers include via holes therein for permitting interconnection of the conductor coils from one layer to the other. Unfortunately, great accuracy may be required in assembling the layers to provide sufficient electrical contact between each vertical conductor and the relatively narrow lateral conductors. In addition, one end of the top coil conductor is exposed adjacent the edge of the chip, and one end of the bottom coil conductor is exposed adjacent another end of the chip so that the conductors can be connected to end terminals.
Conventional chip type, surface mount, ferrite EMI suppressors are commonly manufactured by screen printing a plurality of conductive traces on a relatively rigid base ferrite tape, and positioning a second relatively rigid ferrite tape thereon. The thus formed multilayer structure is heated under pressure to form a monolithic structure. Unfortunately, the conventional screen printing process limits the thickness of the electrically conductive material, typically a silver or other precious metal paste. The thickness of the conductive path may be only 0.2 mils (0.0002- or about 5.0 .mu.m). Accordingly, the current carrying capability of such a device may be severely limited, that is, on the order of only several milliamperes.
Steward Inc., the assignee of the present invention, developed an EMI suppressor for higher currents and including enlarged pads at the ends of U-shaped laterally extending conductors on intermediate ferrite layers. Vertical conductors were provided by one or more solid conductors completely filling an associated vertical opening in the ferrite layer. Top and bottom lateral conductors had end portions connected to respective overall opposing end caps on the ferrite body. Unfortunately, the relatively small dimensions and manufacturing tolerances often made it difficult to mass produce the suppressors having solid vertical conductors without voids.
Notwithstanding the above mentioned references, there continues to exist a need in the art for ferrite EMI suppressors capable of handling relatively large currents. For example, applications such as DC-to-DC converters and disc drives may require suppression of electromagnetic interference at current levels of up to about 6 amps continuously, and to surge levels of about 10 amps. In addition, automated mass production of such devices is also a concern.